Compression tests on motors

[reelchippy]

Guys is there any way that I would be able to check the compression of an motor myself the with some gauge or device cheers

[faulked]

you can buy a compresion guage from ripco or super cheap you remove your spark plugs detach fuel line if you have a safety lanyard pull that so it cant spark and one bye one you get a mate to wind the engine over a few spins and test the compression looking for differences between them or teribly low figures

[Feral]

If it reads low, squirt a small amount of engine oil into the spark plug hole, and redo compression test. if it goes up by more than about 10-15psi, you have worn rings.

[reelchippy]

Thanks guys i also came across this [file name=Assessing_Used_Outboard_Motors.doc size=27136]http://www.australianfishing.com.au/media/kunena/attachments/legacy/files/Assessing_Used_Outboard_Motors.doc[/file]

Assessing_Used_Outboard_Motors.doc

[reelchippy]

I am still on the used boat trail cheers

[Feral]

Not bad, a bit excessive for checking a motor, IE checking the gearbox oil, dont think I'd be to happy about prospective buyer dropping the oil out!

Aso not mentioned , but easy to check - it should pump lots of water!

Also normal push on compression tester should be up to the job, no need for a threaded one.

[reelchippy]

Feral wrote:

Not bad, a bit excessive for checking a motor, IE checking the gearbox oil, dont think I'd be to happy about prospective buyer dropping the oil out!

Aso not mentioned , but easy to check - it should pump lots of water!

Also normal push on compression tester should be up to the job, no need for a threaded one.

Thanks feral

[rumrunner]

get with the times fellas!

compression tests went out in the 90s!

we use leak down tests now! and only use compression testers for a round about sort of guestamate!

a leak down test is ezy and much more accurate at pinpointing if there is ware! and where the fault/ware is.

[Feral]

Yeah but that type of gear is not in the average home handman's tool box, where a $25 compression tester is.

Also I dont trust these new fangled ways

[rayke1938]

You do not need to drain the gearbox to check condition of oil.

Leave the top plug in and just undo bottom plug and leave a small ammount of oil to run out.

Check that no drops of water come out first. ( Caused by worn seals or shaft)

Put a drop on a sheet of white paper and look for bits of metal in it can be either steel or bits of bronze.

If its black will need a oil change but if its milky it has water in it. ( shaft/seals)

If you are looking at a pricy unit would be prudent to pay for an independant inspection.

Ray

Cheers

Ray

[bootyinblue]

I know when I was looking at buying a second hand motor, I was taught that a lot of the bottom drain plugs have a magnetic tip on them obviously to attract any metal particles that were swimming around in the oil. I unscrewed several and 'pinched' the end of the plug and then rubbed thumb and forefinger together to feel for 'grit'. One motor became a thanks, but no thanks based on that.

[rumrunner]

Feral wrote:

Yeah but that type of gear is not in the average home handman's tool box, where a $25 compression tester is.

Also I dont trust these new fangled ways

you prob dont trust them because you dont know how to do it!:blush:

i meant that people should not bother with old comp testers!

get it tested by someone who knows how to use a leak down and knows what they are looking for!

compression testers were forced out in the 90s for a reason! they are not accurate or precice enuff for todays technoligy

but if only for a guideline then whats the harm i suppose

[kriso]

rumrunner wrote:

Feral wrote:

Yeah but that type of gear is not in the average home handman's tool box, where a $25 compression tester is.

Also I dont trust these new fangled ways

you prob dont trust them because you dont know how to do it!:blush:

i meant that people should not bother with old comp testers!

get it tested by someone who knows how to use a leak down and knows what they are looking for!

compression testers were forced out in the 90s for a reason! they are not accurate or precice enuff for todays technoligy

but if only for a guideline then whats the harm i suppose

i would have to disagree i work as a mechanic and still use compression testers even to this date manufacturers ask for compression figures for engine troubles. while i agree leakdowns are more precise i can still diagnose a problem just as easy with a $100 compression tester. not trying to have a go just my look on things as every mechanic has diffrent views on procedures.

[Feral]

Mate my other hobby is car racing - trust me a hot compression test tells me a lot more about my motor than a leak down test would.

For me its all about what you feel in your water, not what the whizbang gizmo says.

[rumrunner]

thanks for your veiw;)

but i dissagree:unsure:

how can you diagnose a fault like a very small head gasket leak with a comp tester?

the tester would just read a bit lower and you would maybe think it needs rings,then pull it down and miss that it was only a bore to water port leak in the head gasket.

or you could have all the compression in the world and still not know you have a hair line crack in the bore or ring lands.

i could keep going but you get my drift.

i do agree that a screw in type (snap on brand)is much better and more accurate then push in 1s but to me they are just a guide line.

and you are rite! all people learn in a diff way and have diff veiws on this matter.

[rumrunner]

Feral wrote:

Mate my other hobby is car racing - trust me a hot compression test tells me a lot more about my motor than a leak down test would.

For me its all about what you feel in your water, not what the whizbang gizmo says.

how do you meen what you feel in your water?

is that a saying or something?

please explain?

ian.

[bootyinblue]

Yep, we get your drift and thanks for the knowledge Rummy. I had never heard of a leakdown test. Is it just as the name implys. Put something in the top and see if it leaks down to the bottom over a period of time.

But the original question was 'is there a way I can check the compression of the engine myself...with some gauge'

A push or screw in dial tester would satisfy this adequately.

[kriso]

rumrunner wrote:

Feral wrote:

Mate my other hobby is car racing - trust me a hot compression test tells me a lot more about my motor than a leak down test would.

For me its all about what you feel in your water, not what the whizbang gizmo says.

how do you meen what you feel in your water?

is that a saying or something?

please explain?

ian.

yeah its a saying sorta like \"going with a gut feeling\"

[rumrunner]

bootyinblue wrote:

Yep, we get your drift and thanks for the knowledge Rummy. I had never heard of a leakdown test. Is it just as the name implys. Put something in the top and see if it leaks down to the bottom over a period of time.

But the original question was 'is there a way I can check the compression of the engine myself...with some gauge'

A push or screw in dial tester would satisfy this adequately.

a leak down is just a simple compressor and a gauge, most people have them.

the test consits of putting the cylinder you want to test to top dead centre and pushing air through,

if putting in 100psi and it says 90 on the pressure gauge then it is 10% leak down! perfect!

if it reads 15% or more you have a problem! you then listen for where the air is escaping, eg: raidiator/pissor,intake or ext if 4stroke!,or carburettors/crankcase if 2 stroke.

pretty ezy;)

i thaught i did answer the question by saying dont bother they are useless.

but that was my oppinion!

sorry it didnt fit with yoursB)

[rumrunner]

i do agree with the gut feeling it never lies.

[kriso]

not looking for an arguement just an opinion from you rummie but whats the diffrence between winding the engine over witha compression guage on it and puttin air in with a leak down test, in my opinion the engine will draw just as much air in to the cylinder as you will be able to put in it if the engine is worn, and with a decent compression tester ( i use a snap-on analog) i would say the diffence between the 2 woube very marginal. would love to hear your side of the discussion

[Lozzel]

I have used both, and I would use a \"Comp tester\" any day over a leak down tester.

All they are good for is collecting dust.

Rummie ,If you ever get a chance to get into the real world, you would learn alot

about diagnostics, without any fandangled tools.

[Fisher_90]

Not everything new is good. Face it, Neither give you and internal look of the cylinders and are just a guide, One has been around for Years the other is a newer way. One could be better than the other but you decide. Me, I'll stay with a comp test.

[rumrunner]

kriso wrote:

not looking for an arguement just an opinion from you rummie but whats the diffrence between winding the engine over witha compression guage on it and puttin air in with a leak down test, in my opinion the engine will draw just as much air in to the cylinder as you will be able to put in it if the engine is worn, and with a decent compression tester ( i use a snap-on analog) i would say the diffence between the 2 woube very marginal. would love to hear your side of the discussion

my opinion is

the differance is when winding ova an engine using a compression tester all you are testing is the compression.

but when using a leak down you can test for allot more eg: head gasket, you will hear air either blowing through to another cyl or out the side or pisser or raidiator if a car,

the simple answer is when using a leak down gauge you can hear! what you are doing and find what you are looking for and pinpoint it ezy, without cranking the engine

i hope that answers the debait:blush:

i dont mean to offend anyone at all but i did run my own shop for 7yrs and i am a qualified mechanicB)

[shortie]

I suppose its like using an oscilloscope rather than manual methods.

Does the same job but a scope will give you more accurate info.

1 instrument that can do many tasks. Old school trained people will always stick to what they know. Thats why we have specialists (guys using motec and other such technology and high perfermance vehicles.

And then the guys still playing with the standard family car.

Unfortunatelly most mechanics these days plug in a computer. Take the error code replace the board charge big $$$ and send you on the way, because they do not know how to diagnose correctly.

Technolgy has its place so does the tried and tested.

A good mechanic uses both methods.

[rumrunner]

so so true shortie!!!

very well said.

thank you!